Field of Invention
The present invention relates to a preparative method of organic compounds, and more particularly to a preparative method for carboxylic acids.
Description of Related Arts
Carboxylic acids are a class of important organic compounds which are widely applied in pesticide, veterinary drugs, medicine industry, and etc. For examples, 4-methanesulfonyl-2-nitrobenzoic acid is a key intermediate in synthesis of Mesotrione, and 4-trifluoromethyl-2-nitrobenzoic acid is a key intermediate in synthesis of Isoxaflutole.
The methods for synthesis of organic acids comprise hydrolysis of carboxylic acid derivatives, haloform reaction, cyano group hydrolysis, oxidation of alcohols or aldehydes, oxidation of alkanes, reaction of carbon dioxide with organo metalic salts.
Carboxylic acid derivatives include esters, amides and acyl chlorides, which are able to prepare carboxylic acid through hydrolysis under alkalic conditions. The yield of this preparative method is moderate to good, and is greatly affected by substrate. Also this preparative method requires pre-introduction of the carboxylic acid derivative functional groups. The method has certain limitation in application.
Haloform reaction is a reaction that a methyl ketone-containing substrate reacts with halogens to produce trihalomethyl ketone. Trihalomethyl ketone then undergoes hydrolysis to produce carboxylic acid. This preparative method has limited reaction applicability due to requirement of specifically structured substrate, and at the meantime produces large quantity of by-products.
Hydrolysis of cyano group under alkalic or acidic conditions is another method for preparing carboxylic acids. For example, o-nitrobenzonitrile undergoes hydrolysis to produce o-nitrobenzoic acid. U.S. Pat. No. 4,868,333 disclosed a method for hydrolyzing 4-trifluoromethyl-2-nitrobenzonitrile to 4-trifluoromethyl-2-nitrobenzoic acid using hydrobromic acid at >100° C. CN101575308 disclosed a method for hydrolyzing 4-trifluoromethyl-2-nitrobenzonitrile to 4-trifluoromethyl-2-nitrobenzoic acid in a good yield using sodium hydroxide in ethylene glycol at <140° C. But the synthesis of the 4-trifluoromethyl-2-nitrobenzonitrile starting material used in the two hydrolysis methods is difficult, which is usually produced by using highly toxic cyanating reagent such as sodium cyanide or copper cyanide to react with 4-trifluoromethyl-2-nitro-halobenzene (CN102675151, EP0994099, EP0758643, U.S. Pat. No. 5,705,674). The yield of the preparative method is not only low yielding with many impurities, but also using highly toxic cyanating reagent resulting in unsafe processing, high production cost and high volumn of industrial wastes.
Another preparative method for carboxylic acids is oxidation of alcohols or aldehydes. Tetrahedron Letters, 2008, 49(15), 2457-2460 reported a method of oxidizing o-nitrobenzyl alcohol with peroxybutanol catalyzed by copper(I) chloride in acetonitrile. WO2003033480 disclosed a method for obtaining o-nitrobenzoic acid using 2-nitrobenzaldehyde via oxidation using sodium perborate in acetic acid. However, the starting material in this process is difficult to obtain.
Benzoic acids is able to be prepared by oxidation of alkyl groups on benzene rings, the oxidizing agent used herein is usually air, potassium permanganate or nitric acid. U.S. Pat. No. 5,591,890 disclosed a method for preparing 4-methanesulfonyl-3-nitrobenzoic acid by oxidizing 4-methanesulfonyl-3-nitrotoluene with air under high pressure, wherein cobalt salt is used as catalyst and acetaldehyde as co-catalyst. CN1090843 disclosed another method for preparing methanesulfonyl-benzoic acid, by oxidizing methanesulfonyl-toluene with nitric acid and air in sulfuric acid in the presence of vanadium or cobalt compounds at 130° C.-170° C. The starting material in this process is not easy to obtain, the methyl group in the starting material is not ready to be oxidized, requiring harsh oxidation conditions, leading to poor oxidation selectivity and low yield.
Another preparative method for benzoic acids is the reaction of o-substituted benzene metal salts with carbon dioxide. Chemische Berichte,1986,119(6),1845-56 reported a method for preparing o-nitrobenzoic acid by reaction between o-nitro-phenyl lithium and carbon dioxide in tetrahydrofuran at low temperature. This reaction is low yielding, due to the interfering of the o-substituted group. Although, this method has its academic values, it is not amenable for industrial production.
In summary, while there are numerous methods reported for the preparation of carboxylic acids, they all have certain problems, limiting their applications, especially in the applications in the field of industrial production.